Frequency conversion apparatus and method

Abstract

A frequency converter, generating an output signal having a frequency of coefficient multiple of a reference clock, comprises a variable oscillator for generating a clock group having phase differences obtained by dividing substantially equally output signal period; a main-phase selector for selecting, from the group, a pair of clocks of desired adjacent phases on a first control signal; a sub-phase selector for selecting, from the pair and a clock phase within the phase difference, the one clock on a second control signal; an operation processor for an operation process by two setting data; a logical controller for generating the control signals on the sub-phase selector clock, the operation processor result, and a phase change control signal; a phase comparator for outputting a phase difference signal between the sub-phase selector and reference clocks; and a controller for controlling the variable oscillator on the phase comparator output.

What is claimed is:  
     
       1. A frequency conversion apparatus which generates an output signal having a frequency equivalent to a coefficient multiple of a frequency of a reference clock signal, said apparatus comprising: 
       a) variable oscillation means for generating a group of clock signals having phase differences obtained by dividing substantially equally a period of the output signal;  
       b) main-phase selection means for selecting and outputting, from said group of the clock signals, a pair of the two clock signals of desired adjacent phases on the basis of a first control signal;  
       c) sub-phase selection means for selecting and outputting, from said pair of the clock signals and a clock phase within the phase difference of these signals, the one clock signal on the basis of a second control signal;  
       d) operation processing means for performing an operation process by using two frequency setting data;  
       e) logical control means for generating the first and second control signals on the basis of the clock signal selected by said sub-phase selection means, the operation result of said operation processing means, and a phase change control signal;  
       f) phase comparison means for outputting a phase difference signal representing a phase difference between the clock signal selected by said sub-phase selection means and the reference clock signal; and  
       g) control means for controlling said variable oscillation means on the basis of the phase difference signal output by said phase comparison means.  
     
     
       2. An apparatus according to  claim 1 , wherein said operation processing means performs a divide of said two frequency setting data, again performs the divide by using the divisor and the remainder of the previous process, and repeats the divide by using the divisor and the remainder of the previous process until the remainder becomes 0. 
     
     
       3. An apparatus according to  claim 2 , wherein said logical control means generates the control signal by using, in the operation process, the quotient in each operation process and the remainder in the process immediately before the last operation process that the remainder becomes 0. 
     
     
       4. An image formation apparatus for performing output control of input image data by using the frequency conversion apparatus defined in  claim 1 . 
     
     
       5. An apparatus according to  claim 4 , wherein said image formation apparatus forms an image by using two beams. 
     
     
       6. An apparatus according to  claim 4 , wherein said image formation apparatus separates the input image data into plural color component data, and forms an image for each color component data. 
     
     
       7. A frequency conversion method which generates an output signal having a frequency equivalent to a coefficient multiple of a frequency of a reference clock signal, said method comprising: 
       a) a variable oscillation step of generating a group of clock signals having phase differences obtained by dividing substantially equally a period of the output signal;  
       b) a main-phase selection step of selecting and outputting, from said group of the clock signals, a pair of the two clock signals of desired adjacent phases on the basis of a first control signal;  
       c) a sub-phase selection step of selecting and outputting, from said pair of the clock signals and a clock phase within the phase difference of these signals, the one clock signal on the basis of a second control signal;  
       d) an operation processing step of performing an operation process by using two frequency setting data;  
       e) a logical control step of generating the first and second control signals on the basis of the clock signal selected in said sub-phase selection step, the operation result of said operation processing step, and a phase change control signal;  
       f) a phase comparison step of outputting a phase difference signal representing a phase difference between the clock signal selected in said sub-phase selection step and the reference clock signal; and  
       g) a control step of controlling the clock signal generation in said variable oscillation step on the basis of the phase difference signal output in said phase comparison step.  
     
     
       8. A method according to  claim 7 , wherein said operation processing step performs a divide of said two frequency setting data, again performs the divide by using the divisor and the remainder of the previous process, and repeats the divide by using the divisor and the remainder of the previous process until the remainder becomes 0. 
     
     
       9. A method according to  claim 8 , wherein said logical control step generates the control signal by using, in the operation process, the quotient in each operation process and the remainder in the process immediately before the last operation process that the remainder becomes 0. 
     
     
       10. An image formation method of performing output control of input image data by using a frequency conversion method defined in  claim 7 . 
     
     
       11. A method according to  claim 10 , wherein said image formation method forms an image by using two beams. 
     
     
       12. A method according to  claim 10 , wherein said image formation method separates the input image data into plural color component data, and forms an image for each color component data.